This is similar to applications' always starting execution with main. Thus, it expects every applet to have these methods, so that it can provide a consistent start-up sequence for each applet. However, the applet container does not know that. Some applets do not use all three of these methods. You might wonder why it is necessary to inherit methods init, start and paint if their default implementations do not perform tasks. The superclass method paint does not draw anything on the applet. The superclass methods init and start have empty bodies, so they do not perform any tasks. If you do not declare these methods in your applet, the applet container calls the inherited versions. In sequence, these three methods are init, start and paint. When an applet container loads class WelcomeApplet, the container creates an object of type WelcomeApplet, then calls three of the applet's methods. Section 20.4 discusses each of these methods in more detail. These methods can be overridden (redefined) to perform tasks that are specific to your applet. Each new applet class you create inherits default implementations of these methods from class JApplet. For this reason, class WelcomeApplet (lines 617) extends JApplet.Īn applet container expects every Java applet to have methods named init, start, paint, stop and destroy, each of which is declared in class JApplet. An applet container can create only objects of classes that are public and extend JApplet (or the Applet class from early versions of Java). As with applications, every Java applet contains at least one public class declaration. Class JApplet (imported at line 4) from package javax.swing is used to create applets. Line 3 imports class Graphics to enable the applet to draw graphics, such as lines, rectangles, ovals and strings of characters. Sample outputs of the WelcomeApplet in Fig.

(This item is displayed on page 965 in the print version)ģ import // program uses class GraphicsĤ import // program uses class JAppletĦ public class WelcomeApplet extends JAppletġ1 // call superclass version of method paintġ4 // draw a String at x-coordinate 25 and y-coordinate 25ġ5 g.drawString( 'Welcome to Java Programming!', 25, 25 ) įigure 20.7. At the end of this section, you will learn how to execute the applet in a Web browser.

Figure 20.7 shows this applet executing in two applet containersthe appletviewer and the Microsoft Internet Explorer Web browser. 20.6) that draws 'Welcome to Java Programming!' on the applet. Examples in Chapters 21, 23 and 24 demonstrate building an applet's graphical user interface. In this chapter, we will demonstrate drawing on an applet. Every Java applet is a graphical user interface on which you can place GUI components using the techniques introduced in Chapter 11 or draw using the techniques demonstrated in Chapter 12.

Make applet dimensions in applet viewer